The 40-year-old actress shot scenes for 'Iron Man 3' in which she wore her co-star's famous suit, and expected to need a lot of mental preparation beforehand after seeing the "hell" the actor went through whenever he donned the restrictive garments - but then couldn't understand why he found it so traumatic.

She said: "I get to do a bit of action and I get to wear the Iron Man suit for a while - it's very cool.

"It's quite cumbersome but not so bad. I thought it was going to be terrible because in the first two movies Robert would put on the suit and start sweating, he'd have a nervous breakdown and would meditate and cry. He was in hell.

"So, I was like, 'Wow, I'd better start mentally preparing myself for the suit,' and I put it on and was like, 'This guy is a wimp, it's really not that bad.' "

The actress - who has children Apple, eight, and Moses, seven, with husband Chris Martin - says her young son particularly enjoyed seeing her as Pepper Potts wearing the suit.

She told Graham Norton in a TV interview airing in the UK tonight (19.04.13): "I'll never forget his face when he saw me walk out in the suit. It was a really good moment."

And Gwyneth is taking great delight in watching Moses figure out how famous she is.

She said:"I love watching his seven-year-old brain put together who I am. We were at a Justin Bieber concert and Moses said, 'Maybe Justin knows who you are from Iron Man.'"